An electrophoresis is a general analytical technique widely used in various industrial fields for fundamental researches and various examinations in biochemistry. Among many of such apparatuses, a horizontal submarine electrophoresis apparatus has been used for the analysis of nucleic acids. This horizontal submarine electrophoresis apparatus comprises a simple structure comprising a cathode and an anode set on the bottom of a box type electrophoresis tank, and a power supply. In addition, a transparent lid for safety purposes is generally set on the top part of the electrophoresis tank.
Such electrophoresis apparatus is conventionally associated with inevitable occurrence of water vapor during electrophoresis due to a temperature elevation of a buffer, and the lid becomes cloudy and bedewed, making the observation of the inside of the electrophoresis tank extremely difficult. For example, under an ordinary temperature, the inside becomes completely invisible within 5 minutes after initiation of the electrophoresis.
When the lid is opened, moreover, a power supply part may become wet due to water droplets from the lid, possibly creating a dangerous situation. In addition, there have been safety and structural problems, since the operator may use the device with the lid open for easy operation during use. Inasmuch as the lid is of the similar size with the electrophoresis tank, a space should be secured to temporarily place the lid once it is removed. The electrophoresis tank is inevitably placed on the operator's side of the working table for the convenient addition of samples, and the power supply therefore is set in the rear part of the working table, which is on the distal end from the operator. Thus, the power cords connecting the both and the lid are placed in between the electrophoresis tank and power supply, and when the lid carries water, it could wet the power supply. Particularly when plural electrophoresis apparatuses are used simultaneously, a wide space on the working table is occupied and the power supply may become wet due to water droplets from the lid, thereby increasing the risk of electric leakage and electrification.
On the other hand, various attempts have been heretofore made to prevent electrification upon lid opening during operation. For example, a power cord may be connected to a lid which, once opened, cuts conductivity from the power supply. Alternatively, a power cord may be set only when the lid is shut, and the lid may not open unless the power cord is removed. These methods, nevertheless, degrade the operability of the apparatus to a greater degree.
While the size of the electrophoresis tank to be employed according to the object varies, a lower service voltage or a greater distance between the cathode and anode produces better resolution. The resolution is generally expressed by the following relational formula: EQU Resolution (.phi.)=.kappa.V (voltage)/D (distance between electrodes) (V/cm )
wherein .kappa. is a constant which is determined by the concentration of agarose gel, kind of buffer, temperature and the like.
The distance between the cathode and anode is practically determined according to the size of the electrophoresis tank, and the service voltage is determined in relation to the migration time. The resolution (.phi.) is in inverse proportion to the migration time. The electrophoresis is practically carried out to achieve a certain range of resolution, and the resolution is controlled by the service voltage.
The electrophoresis apparatus for a minigel is widely used for its rapid performance rather than the resolution. For the assays of DNA and determinations of reactions, a long migration distance is not necessary, nor is the resolution required. Thus, an electrophoresis apparatus for minigel mostly suffices for general use.
However, an accurate determination of the molecular weight by electrophoresis requires a certain distance between electrodes, thus necessitating a large electrophoresis tank. The use of such large electrophoresis tank instead of an electrophoresis apparatus for minigel is disadvantageous in that the long distance between electrodes requires high voltage, while a power supply therefor is difficult to secure and even more dangerous. Therefore, at least two kinds of large and small electrophoresis tanks have been needed for routine analysis.
It is therefore an object of the present invention to provide a safe electrophoresis apparatus generally used in wide applications, such as a horizontal submarine electrophoresis apparatus, wherein the lid of a migration tank does not suffer from clouding or bedewing due to the water vapor generated during electrophoresis, thus permitting an easy observation of the inside of the electrophoresis tank without opening the lid, but through it.
Another object of the present invention is to develop an electrophoresis apparatus capable of both an accurate electrophoresis and a rapid electrophoresis using a minigel.